Bile pigments in plants and animals are structurally related by virtue of their common origin from the carbon skeleton of protoporphyrin IX, but otherwise distinct in two fundamental ways. First, plant bile pigments serve as photoreceptors for a host of light-mediated processes required for growth and development whereas mammalian bile pigments are potentially toxic, transient elimination products of hemoglobin catabolism with no known function. Second, plant bile pigments are covalently attached to apoproteins and the resulting chromophore-apoprotein inter-action, renders them stable to photo-oxidation in vivo. In contrast, mammalian bile pigments form non-covalent bonds, (ionic, hydrophobic) with proteins (eg. albumin, ligandin) and their instability in light is the basis of phototherapy in neonatal jaundice. Phycobiliproteins are light-harvesting photosynthetic pigments in red and blue-green algae. The bile pigment prosthetic groups of these pigments are phycocyanobilin and phycoerythrobilin, which are structural analogs of biliverdin and bilirubin in mammals. This project is concerned with synthesis of algal bile pigments, the primary structure of the apoproteins to which algal bile pigments are attached, and coordinate regulation of bile pigment and apoprotein synthesis during formation of phycobiliproteins. During heme conversion to bile pigment, two oxygen atoms not present in precursor heme are inserted into the macrocycle and the mechanism of this reaction will be studied by measuring 18, 1802 incorporation into phycoerythrobilin. The primary structure of the phycobiliprotein, allophycocyanin, will be determined by automated sequential degradation to better understand the functional significance of bile pigment-apoprotein interaction in vivo. Translation of the mRNAs for the apoproteins of phycobiliproteins in a cell free system will be investigated using wild-type cells and pigment mutants, to determine some of the events involved in expression of the genes for phycobiliproteins in vivo.